1. Field of the Invention
The present invention relates generally to liquid crystal display devices. More particularly, the invention is directed to liquid crystal display devices including preventive measures against changes in gap between substrates and against displacement of the substrates in directions of respective principal planes, the display devices further containing a necessary measure to prevent spacers from damaging alignment films.
2. Description of the Related Art
In liquid crystal display devices, a thin-film transistor (TFT) substrate, on which a pixel electrode, thin-film transistors (TFTs), and other elements are formed in a matrix format, and a counter substrate are arranged with liquid crystals sandwiched between the TFT substrate and the counter substrate. A transmittance of the light, as passed through the liquid crystal molecules, is controlled on a pixel-by-pixel basis to form an image. On both the TFT substrate and the counter substrate, an alignment film for initially aligning the liquid crystals is formed on the contact surface where the substrate comes into contact with the liquid crystals.
A method of forming a columnar spacer below the counter substrate is used to prevent changes in distance (hereinafter referred to as the gap) between the TFT substrate and the counter substrate; that is, changes in layer thickness of the liquid crystals. After the liquid crystal display device has been fabricated to completion, an external pressure applied to the counter substrate during operation of the device shifts both the TFT substrate and the counter substrate to the directions of respective principal planes (hereinafter, these relative shifts will be referred to simply as the displacement of the TFT substrate and the counter substrate). Forming the columnar spacer only below the counter substrate to control the gap often poses a problem in that the columnar spacer has its distal end damaging the alignment film formed over the TFT substrate.
To deal with this problem a configuration with both a columnar spacer provided below a counter substrate and a columnar spacer support base disposed above a TFT substrate is developed to control the gap between both substrates (the columnar spacer support base will hereinafter be referred to simply as the base). Since only a very thin alignment film is formed on the base, although the alignment film may be damaged by the columnar spacer, adverse effects of the damage will be insignificant. The columnar spacer used in this case would be circular or square in a shape of a planar section and trapezoidal in section, and the base would also have a planar shape that fits the planar shape of the columnar spacer.
Nonetheless, other problems may arise. One problem is that if the counter substrate and the TFT substrate are significantly displaced, the columnar spacer may fall off the base, thus damaging the alignment film in a display region. Another problem is that even after the external force upon the liquid crystal display device has been removed, the columnar spacer may become stuck in the base and fail to return to an original position in the base, which may then keep the counter substrate and the TFT substrate out of alignment.
JP-2013-186148-A describes a configuration in which two spacers, one close to a counter substrate and the other to a TFT substrate, having a rectangular plane and offset by 90 degrees in an angle of a long axis relative to each other are arranged to prevent an event of a columnar spacer falling off a base.